Simulation on parameter optimization of semiconductor ring resonator with nano-antenna for heat-assisted magnetic recording device

Optical Review - Heat-assisted magnetic recording (HAMR) is a promising technology with high recording density. The authors’ group has proposed a novel device for HAMR, in which a metal...     

Simulation on parameter optimization of gold nano-antenna attached to semiconductor ring resonator for heat-assisted magnetic recording device

Heat-assisted magnetic recording is a technology to improve recording density for hard disks. The authors’ group has proposed a device, in which a gold nano-antenna as a near-field transducer is attached to a semiconductor ring resonator as an integrated light source. Localized surface plasmon resonance at the tip of nano-antenna excites near-field light to form small recorded marks to increase recording density. In this study, to improve the device performance, the dependence of spot size and energy density of near-field light on tip curvature, length, and bottom diameter of nano-antenna was investigated through a numerical simulation. Cylinder type and cone type nano-antennas were considered. For both types, as the tip curvature of nano-antenna increased, the spot size decreased and the energy density increased. It was possible to reduce the spot size to 18 × 18 nm². For cylinder type, there was an optimal length of nano-antenna where the energy density became maximum, and the optimal length changed depending on the presence or absence of recording medium. This was because of the difference in plasmon resonance condition. Moreover, for cone type, there was an optimal bottom diameter of nano-antenna where the energy density became maximum, and the optimal bottom diameter changed depending on the length of nano-antenna.

     

Micromagnetic modeling for heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is one of the candidate systems beyond the perpendicular recording technology. Here, a micromagnetic model and a heat transfer model are introduced to study the heating and cooling processes in the HAMR media; then, by integration of the SPT head and the laser heating source, the recording performance is simulated and investigated on a single track at an area density of 1 Tb/in². In the HAMR system, the temperature in the medium under the laser wave guide is increased by heating, and decreased by air bearing and heat conduction when the write process really occurred. The target of this study is to find the proper design of the head-laser assembly for optimum recording. It is found that the proper distance between the laser wave guide and the head's main pole rear/front edge is only 41.4/1.4 nm for optimum recording performance.     

Simulation on near-field light on recording medium generated by semiconductor ring resonator with metal nano-antenna for heat-assisted magnetic recording

Optical Review - Heat-assisted magnetic recording (HAMR) is a promising technology for achieving more than 10 Tbit/inch2 recording density. A near-field transducer (NFT), which forms a small light...     

Simulation on near-field light generated by metal nano-dot on GaAs substrate for heat source of heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is promising for achieving more than 1 Tb/inch² recording density. A near-field transducer (NFT), which forms a hot spot of 10–100 nm in diameter on a recording medium, is necessary in HAMR. In this study, localized surface plasmons generated by a metal nano-dot in a novel device for a heat source of heat-assisted magnetic recording were analyzed using a simple model in which a metal hemisphere was formed on a GaAs substrate and a quasi-electrostatic approximation. The scattering and absorption efficiencies as well as the enhancement factor were investigated for several kinds of metal. As a result, their dependence on the wavelength and the polarization direction of the incident light was clarified.     

Characterization of heat-assisted magnetic probe recording on CoNi/Pt multilayers

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm on the film fabricated on bare silicon substrate when the pulse voltage is above a threshold voltage. The mark size becomes 260 nm when they are written on the identical film fabricated on an oxidized silicon substrate. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. A synthesized model, which contains the calculation of the emission current, the simulation of heat transfer during heating, and the study of magnetic domain formation, was introduced to explain experimental results. The simulation agrees well with the experiments.     

Characterization of media cross-track thermal profile in heat-assisted magnetic recording

In the heat-assisted magnetic recording, the thermal profile of the media affects the recording performance seriously. Unfortunately, there is no direct method to measure it dynamically. In this paper, an indirect method is proposed to characterize the cross-track thermal profile with the spin-stand. The experimental results indicate that the local temperature increase has nonlinear relationship with the laser power. As the laser power increases, the thermal profile width increases. The media has a higher temperature increase and a bigger thermal profile at a slower rotation speed. The reasons for these phenomena are explained as well.     

FePt-C granular thin film for heat-assisted magnetic recording (HAMR) media

We studied a FePt-C granular film for ultra-high density perpendicular recording media towards 1 Tbits/in.² because of strong magnetocrystalline anisotropy at its L1₀-phase. We deposit a Fe₅₂Pt₄₈-C50 % (6.7 nm) film on oxidized silicon substrates at 400 °C and 0.50 Pa Ar pressure. The perpendicular anisotropy of the film is 20 kOe, with a perfect squareness of 1. Bright-field transmission electron microscopy (TEM) images display that the FePt granular film has small and uniform grains of 6.4 ± 1.5 nm. Further work on high-resolution TEM imaging demonstrates excellent L1₀ ordering for this FePt granular film, which is consistent with the texture measurement by X-ray diffraction. Thus, we prove that FePt granular film is a promising candidate for high-density heat-assisted magnetic recording media.     

The role of nucleation field of media in heat-assisted magnetic probe recording

We characterize a method of heat-assisted magnetic probe recording on perpendicular media. Heating source is field emission current from a scanning tunneling microscope (STM) tip. Recording media are three kinds of magnetic films, Co/Pt, CoNi/Pt, and Co/Pd multilayers with different nucleation fields. Pulses with amplitude of 5 V were applied between the STM tip and the recording medium. Experiments show that magnetic marks with an average size of 180 nm were formed on both Co/Pt and CoNi/Pt films whose nucleation fields are greater than their saturation magnetization. No marks were observed on the Co/Pd film whose nucleation field is smaller than its saturation magnetization. A model is built to simulate the dynamic process of domain formation in probe-based magnetic recording system. Simulation results agree with experiments and it explains the effect of the nucleation field of medium in perpendicular recording.     

Dependence of mark size on STM pulse voltage in heat-assisted magnetic probe recording on a cobalt–nickel–platinum thin film

This paper presents a method of heat-assisted magnetic probe recording on perpendicular medium. Electrical current from scanning tunneling microscope (STM) is employed as the major heating source. Recording medium is a strongly-coupled CoNi/Pt multilayered film. Pulses with amplitude of 3–7 V and duration of 200 ns were applied between the STM tip and the recording medium. Experiments show that magnetic marks with an average size of 184 nm were formed for voltages above 4 V. A model is built to simulate the formation of magnetic domains in the processing of probe-based magnetic recording. Simulation results agree with experiments well.     

Heat-treatment effect on structure and magnetic properties of hard magnetic Co-W films for perpendicular magnetic recording

The variations of coercivity for different preferred orientation (PO) of electrodeposited Co-W films with perpendicular magnetic anisotropy are demonstrated by manipulating the inter-particle separation through the heat-treatment effect. The character of the dependences corresponds to magnetization reversal of the films with (002) PO by the rotational mechanism.     

Non-stoichiometric barium ferrite particles for high-density magnetic recording

The organometallic precursor method was employed for the synthesis of β” ferrites, from which non-stoichiometric Ba ferrite particles have been prepared by ionic exchange. The magnetic grains are hexagonal platelets with diameters as low as 50 nm and aspect ratio of 1.5. After annealing, the sample diameter increases to 200 nm while the grains remain single-domain. The Curie temperature is 455°C. Annealed samples show specific magnetization up to 62 emu/g, coercive fields _jH_c close to 2 kOe, and an SFD factor 1−S* of 0.55     

Prospects for bit patterned media for high-density magnetic recording

Prospects for bit patterned media (BPM) of more than 1 Tb/in² are discussed. Improvement in the pattern drawing for small feature size and high precision is necessary for fabrication process. Deviation in the magnetic properties should be estimated and reduced. The etching damage seems not to be large. Design of the substructure of the magnetic dot is necessary for reducing the deviation. BPM is also a good template for technologies to increase the recording density. Combination of BPM with heat-assisted recording or exchange-coupled layers is advantageous for high-density recording.     

Double-layer particulate magnetic recording media

Double-layer media employ two layers with different magnetic characteristics, with the objective of optimizing performance and/or reducing the overall cost. The idea has recently been applied to longitudinally oriented thin top layers of Ba-ferrite (BF) or metal particle (MP) coated over thicker Co-iron oxide (CoFe) or non-magnetic (NM) underlayers resulting in significantly improved recording performance for high recording density video, digital audio and data applications.     

Sm–Co films for high-density magnetic recording media

In this experiment, Cr–Cu thin film was used as an underlayer for Sm–Co film. The magnetic properties and crystal structure of Sm–Co films prepared onto this kind of underlayer have been studied. Grain size and surface roughness have been reduced with the introduce of Cr. The Cr addition into the Cu underlayer also improves the c-axis orientation of Sm–Co films. As a result, films with squareness ratio as high as 0.95 and perpendicular coercivity as high as 12.3 kOe have been prepared.     

Research and development of metal powder for magnetic recording

Since its first application within the compact cassette in 1978, magnetic recording media using metal powder have been improved at a rate of roughly 1 dB per year as a result of advances in such fields as tape materials, tape-making technologies, etc. Today, metal tapes have a widely expanded application area, including video and data-information applications. Dowa Mining Co., Ltd., began its research regarding magnetic powder for recording media in 1978. The Company successfully developed metal powder for 8 mm video tape. Since then, Dowa has endeavored to improve the magnetic properties and reduce the particle size of metal powder. It accomplishes these goals through the full use of the Company's unique Al doping method. Especially, during the past several years, significant improvements of the magnetic properties of metal powder have been achieved. These improvements have resulted from the introduction of new technologies, including Fe–Co alloying, sintering prevention, new reaction processes, and many other new techniques. Currently, Dowa Mining is supplying a new type of metal powder for the most technologically advanced high-density recording media. Dowa's new metal powder has an axis length of 0.1 μm, H_c of 2400 Oe, and σ_s of 155 emu/g.     

Role of magnetic circular dichroism in all-optical magnetic recording

Using magneto-optical microscopy in combination with ellipsometry measurements, we show that all-optical switching with polarized femtosecond laser pulses in ferrimagnetic GdFeCo is subjected to a threshold fluence absorbed in the magnetic layer, independent of either the excitation wavelength or the polarization of the laser pulse. Furthermore, we present a quantitative explanation of the intensity window in which all-optical helicity-dependent switching (AO-HDS) occurs, based on magnetic circular dichroism. This explanation is consistent with all the experimental findings on AO-HDS so far, varying from single- to multiple-shot experiments. The presented results give a solid understanding of the origin of AO-HDS, and give novel insights into the physics of ultrafast, laser controlled magnetism.